JPS58206057A - Nonaqueous electrolyte battery - Google Patents

Abstract

PURPOSE:To improve voltage drop in initial discharge stage and increase discharge capcity by adding to a positive electrode noncovalent bond graphite intercalation compound intercalating metal fluoride and fluorine between graphite layers. CONSTITUTION:A light metal as a negative active mass, nonaqueous solution prepared by dissolving an inorganic salt in an organic solvent as an electrolyte, and graphite fluoride as a positive active mass are used. Noncovalent bond graphite intercarlation compound intercalating metal fluoride and fluorine between graphite layers is added to the positive electrode. Graphite fluoride having larger electrochemical equivalent is used as a main active mass, and CeF(MFm)n having good conductivity and reactivity as active mass, and high potential is added to the positive electrode, and a battery is assembled. Removal or decrease of nonreactive conductive mass, capacity increase by discharge reaction of CeF(MFm)n, and mixed potential of both active mass improve voltage performance in initial discharge stage. Graphite fluoride is nonconductive before discharge but becomes conductive by discharge inorder to form graphite, then conductivity of the positive electrode is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses light metals such as lithium, sodium, aluminum, and magnesium as a negative electrode, and lithium borofluoride as an aprotic organic solvent such as γ-butyrolact/, dimethoxyethane, and propylene carbonate as an electrolyte. Using a non-aqueous electrolyte in which an inorganic salt such as lithium perchlorate is dissolved, graphite fluoride ((CF) is used as the main active material of the positive electrode.
This article relates to an additive to the positive electrode of a non-aqueous electrolyte battery using SO<1≦1.

The positive electrode active material of this battery, 7] graphite, is chemically extremely stable, has a large electrochemical equivalent, and has a discharge reaction ((
CF)n+ne-n(:+nF-) generates carbon with good conductivity, so it has high energy density and good storage properties, and internal resistance does not increase easily even in the latter half of discharge.
It is known as a material that is extremely suitable for constructing batteries with a flat discharge voltage.

In addition, fluorinated graphite belongs to the covalent graphite intercalation compound and is non-conductive, so when composing the positive electrode, a conductive agent is mixed in to conduct the electronic conduction of the positive electrode, as is the case with many positive electrode active materials. It is necessary to give gender.

Usually, carbon powder is added in an amount of 6 to 20% of the weight of the positive electrode, mixed with a binder, and molded, but at this time, the volume occupied by the conductive agent is as much as 30% of the positive electrode. There is still room to increase the capacity by increasing the amount of active material filled. In addition, among the discharge characteristics of the fluorinated graphite positive electrode, the initial discharge voltage is slightly unstable, which requires improvement.
There is a phenomenon in which the -po voltage drops at 1 when the -po voltage reaches the flat voltage.

Although there is still no established theory as to the cause of this behavior, there is a theory that the influence of the discharge reaction of >CF2-cv3 groups present in the outer layer of the fluorinated graphite molecules is dominant in the initial stage of discharge. Putting aside the cause, methods have been proposed to improve it, such as adding active materials with a relatively high initial voltage such as manganese dioxide, but these interact with fluorinated graphite during storage and degrade performance. There was a problem.

The present invention aims to solve the above-mentioned problems of nonaqueous electrolyte batteries using fluorinated graphite as the main active material of the positive electrode, that is, to improve the drop phenomenon of the initial discharge voltage and further increase the discharge capacity. .

The present invention uses a material that serves as a conductive agent and an auxiliary active material in the positive electrode of the battery, and has a discharge voltage slightly higher than that of fluorinated graphite, that is, non-covalent graphite in which metal fluoride and fluorine are inserted between graphite layers. By adding an intercalation compound, the initial discharge voltage is improved and the discharge capacity is increased.

The above graphite intercalation compound is obtained by heating metal fluoride and carbon in the presence of fluorine gas.
)n (M is a non-transition element, 2m is its valence). Other non-covalent graphite intercalation compounds include CeM'Fm.
(M' is a transition element), and both are attracting attention as materials with much higher conductivity than carbon, and the latter is chemically unstable in the atmosphere, making it difficult to handle and use as a battery material. However, the former is chemically stable and has fluorine between its layers, which reacts as an active material in batteries, and its theoretical discharge capacity is smaller than that of fluorinated graphite. Although it is not very attractive as a single active material, it is characterized by a slightly high discharge potential and stability from the initial stage of discharge. Typical examples of CeF(MFm) n-type compounds mentioned in F are CeF(AQF)n,
There are materials such as CeF(MgF2)n, and the discharge characteristics of these and graphite fluoride are compared in an organic electrolyte using lithium as a counter electrode, and a typical conceptual diagram is shown in FIG. 1.

In Figure 1, A is C@F(MFm), B is (CF)n
The above-mentioned difference in discharge characteristics between the two can be understood as a qualitative concept.

Both active materials have in common that only fluorine is involved in the discharge reaction, and since they are chemically stable materials, self-depletion reactions occur even when both are mixed and stored in the positive electrode. CeF is relatively high potential during discharge.
Although the discharge of (MFm)n takes priority, the discharge of (CF)n proceeds in parallel and shows a hybrid potential, making it possible to increase the voltage at the initial stage of discharge compared to when (CF)n is used alone. I can do it.

The present invention uses fluorinated graphite and CeF (MF
'm) It was established by focusing on the properties of 11, taking advantage of the strengths of both, and compensating for the weaknesses.The main active material is graphite fluoride, which has a large electrochemical equivalent, and has good conductivity. Ce reacts as an active material and has a high potential
By constructing a battery using a positive electrode to which F(MFm)n is added, it is possible to omit or reduce the amount of non-reactive conductive agents such as carbon, increase the capacity due to the discharge reaction of CeF(MFm)n, and increase the capacity of both. This improves the initial discharge voltage characteristics due to the mixed potential of the active material. In addition, although fluorinated graphite is nonconductive in the undischarged state, it generates carbon during discharge and improves the conductivity of the positive electrode.
Ce(LiF)(MFm) which is a discharge product of Fm)n
Since n also has conductivity that is not much different from that in the undischarged state, the internal resistance of the battery can be maintained low even from the latter half to the final stage of discharge, and flat voltage characteristics with little final voltage drop can be obtained.

FIG. 2 is a sectional view of a battery constructed to experimentally confirm the effects of the present invention. In Fig. 2, 11 is a sealing plate made of stainless steel, 2 is a negative electrode current collector net made of the same material welded to 1, 3 is a lithium negative electrode crimped to 2, 4 is a separator made of polypropylene nonwoven fabric, and 5 is a 7-hole graphite (
(CFx)n) as the main component, fluororesin powder and CeF(
MFm)n and acetylene plaque are mixed and pressure-molded in various proportions as described below, and a positive electrode 6 is press-fitted into the positive electrode 5 with an IF electrode current collector net made of titanium. 7 is a battery case made of stainless steel, 8 is a gasket made of polypropylene, and the sealing is accomplished by folding the opening of the battery case 7 inward. Inside the battery, 1 mole of lithium borofluoride was added to a solvent mixed with propylene carbonate and dimethoxyethane at a volume ratio of 1=1.
A dissolved electrolyte is injected.

A battery with the above configuration with a diameter of 20 mm and a thickness of 1.6 mm,
Prototypes were made with various positive electrode formulations as shown in the table below.

Figures 3 and 4 show batteries A to I at a temperature of 20°C.
, shows the results of constant resistance discharge at 30 kQ. In FIG. 3, (CF)n is used as a positive electrode material, and 06F (AnF3) is used. , 1. Or 03F (
MgF2). ,. This is a comparison diagram of various additive amounts of No. 3. The larger the amount added, the higher the initial heart pressure, and the improvement effect is remarkable. Further, if the amount added is less than 30 M It, the discharge capacity increases, but if it is more than 46 M It, the capacity decreases. The optimal combination of impurities differs depending on the characteristics required of the battery, but generally the discharge voltage is high, the voltage flatness is affected, and it is preferable to have something that is unforgiving, so it should be 5 to 30% by weight. considered appropriate. Furthermore, from the comparison of A and F, it can be interpreted that there is no significant difference in the effect of addition between the two types of additives.

Figure 4 shows the effect of adding an active material and conductive agent when (CF., 7)n is used as a living material, and it is a mixture of (CF)n and (02F)n (<1:' For Fo, 7) n, the same improvement effect as in FIG. 3 was obtained using (cp', )= as the main active material.

As described above, the effects of the present invention are extremely significant. No.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of the discharge characteristics of CeF(MFm)n and (CF)n as positive electrode active materials, Figure 2 is a cross-sectional view of a battery constructed to confirm the effects of the present invention, and Figure 3'e. and fourth
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Claims (1)

[Claims] (1) A light metal was used as the negative electrode active material, a non-aqueous solution of an inorganic salt dissolved in an organic solvent was used as the electrolyte, and fluorinated graphite was used as the main active material of the positive electrode, and metal fluoride and 7 elements were inserted between the graphite layers. A non-aqueous electrolyte battery with a non-covalent graphite intercalation compound added to the positive electrode. 2. The nonaqueous electrolyte battery according to claim 1, wherein the amount of the non-covalent graphite intercalation compound added is 5 to 30% of the weight of the positive electrode.